Furfuryl alcohol is generally produced by catalytic hydrogenation of furfural in a vapor or liquid phase using copper catalysts. Thus, British Pat. No. 734,118 teaches hydrogenation in a vapor phase at a temperature of from 80.degree. to 200.degree. C. in the presence of a copper catalyst containing 50 to 20% of anhydrous sodium silicate. FRG Pat. No. 835,148 teaches the use, as the catalyst, of copper supported on an alkali metal silicate or silicic acid, while FRG Pat. No. 881,544 discloses the use of copper-silicate catalysts promoted with oxides of elements pertaining to Group II of the Periodic System. French Pat. No. 2,250,099 discloses the use of an alloyed copper-aluminum catalyst for hydrogenation of furfurol in the presence of a hydrogenation agent, i.e. gases of the synthesis of ammonia, at a temperature ranging from 100.degree. to 150.degree. C.
Also known in the art is a method (cf. Polish Pat. No. 67674) for preparing furfuryl alcohol and sylvan in the presence of a copper-chromite catalyst promoted with oxides of calcium, barium or zinc at a temperature within the range of from 100.degree. to 300.degree. C. under a pressure of 1 atm or more. Polish Pat. No. 77554 teaches hydrogenation of furfurol with the introduction of a polymerization inhibitor, i.e. triethanolamine. Carrying out processes of hydrogenation of furfural in a vapor phase necessitates the use of cumbersome apparatus due to circulation of a large amount of gaseous compounds in the system. Furthermore, great losses of furfuryl alcohol occur due to polymerization thereof at high temperatures along with the formation of a considerable amount of by-products, as well as lowering of the catalyst activity due to resinification thereof with the polymerization products.
Carrying out the process in a liquid phase eliminates evaporation of furfural and related (due to polymerization) losses; also avoided is the necessity of circulating large volumes of hydrogen. The liquid-phase processes may be exemplified by those described in Patents of Czechoslovakia, France, Hungary and USA. Thus, Czechoslovakian Pat. No. 144018 teaches hydrogenation of furfural under a pressure ranging from 10 to 250 atm and at a temperature of from 70.degree. to 210.degree. C. on a catalyst prepared at a uniform atomic distribution of copper on acidic silica neutralized with sodium or potassium. However, catalysts containing copper supported on a carrier are usually less active than copper-chromite ones.
French Pat. No. 2,275,471 teaches hydrogenation of furfural with hydrogen or hydrogen-containing gas at a temperature ranging from 100.degree. to 160.degree. C. on a catalyst including metallic copper, oxides of metals of Group II and/or Group III of the Periodic System, as well as sodium oxide and a neutral agent, i.e. graphite. Furfural is added to the reactor while being diluted with the reaction products.
However, dilution of furfural with the reaction products, namely with furfuryl alcohol, results in a lowered yield of the desired product due to an additional polymerization of furfuryl alcohol.
Known in the art is a process for preparing furfuryl alcohol by hydrogenation of furfural at a temperature within the range of from 170.degree. to 200.degree. C. under a pressure of from 150 to 220 atm using a suspended copper-chromite catalyst promoted with oxides of metals of Group II (cf. Hungarian Pat. No. 147519).
This prior art process has a disadvantage in its use of high pressure and an additional operation of separating of the catalyst from the reaction products. This operation causes additional losses and is economically inefficient.
Also known in the art is a process for producing furfuryl alcohol in a liquid phase in the presence of a copper-chromite catalyst promoted with oxides of Group II metals at a temperature within the range of from 90.degree. to 175.degree. C. under a pressure of from 30 to 200 kgf/cm.sup.2 (400 to 3,000 pounds/sq.in) (cf. U.S. Pat. No. 2,094,975). This process features hindered removal of the reaction heat causing a spontaneous elevation of the reaction temperature. This causes the formation of byproducts which lower purity of the resulting furfuryl alcohol and reduce the catalyst activity.